Method and system for microwave excitation of plasma in an ion beam guide

ABSTRACT

An apparatus and method for providing a low energy, high current ion beam for ion implantation applications are disclosed. The apparatus includes a mass analysis magnet mounted in a passageway along the path of an ion beam, a power source adapted to provide an electric field in the passageway, and a magnetic device adapted to provide a multi-cusped magnetic field in the passageway, which may include a plurality of magnets mounted along at least a portion of the passageway. The power source and the magnets may cooperatively interact to provide an electron cyclotron resonance (ECR) condition along at least a portion of the passageway. The multi-cusped magnetic field may be superimposed on the dipole field at a specified field strength in a region of the mass analyzer passageway to interact with an electric field of a known RF or microwave frequency for a given low energy ion beam. The invention further comprises a mass analyzer waveguide adapted to couple the electric field to the beam plasma consistently along the length of the mass analyzer passageway to thereby improve the creation of the ECR condition. The invention thus provides enhancement of beam plasma within a mass analyzer dipole magnetic field for low energy ion beams without the introduction of externally generated plasma. The invention further includes a method of providing ion beam containment in a low energy ion implantation system, as well as an ion implantation system.

FIELD OF THE INVENTION

The present invention relates generally to ion implantation systems, andmore specifically to an improved method and system for microwaveexcitation of plasma in an ion beam guide.

BACKGROUND OF THE INVENTION

In the manufacture of semiconductor devices, ion implantation is used todope semiconductors with impurities. Ion beam implanters are used totreat silicon wafers with an ion beam, in order to produce n or p typeextrinsic materials doping or to form passivation layers duringfabrication of an integrated circuit. When used for dopingsemiconductors, the ion beam implanter injects a selected ion species toproduce the desired extrinsic material. Implanting ions generated fromsource materials such as antimony, arsenic or phosphorus results in “ntype” extrinsic material wafers, whereas if “p type” extrinsic materialwafers are desired, ions generated with source materials such as boron,gallium or indium may be implanted.

Typical ion beam implanters include an ion source for generatingpositively charged ions from ionizable source materials. The generatedions are formed into a beam and directed along a predetermined beam pathto an implantation station. The ion beam implanter may include beamforming and shaping structures extending between the ion source and theimplantation station. The beam forming and shaping structures maintainthe ion beam and bound an elongated interior cavity or passagewaythrough which the beam passes en route to the implantation station. Whenoperating an implanter, this passageway must be evacuated to reduce theprobability of ions being deflected from the predetermined beam path asa result of collisions with air molecules.

The mass of an ion relative to the charge thereon (e.g., charge-to-massratio) affects the degree to which it is accelerated both axially andtransversely by an electrostatic or magnetic field. Therefore, the beamwhich reaches a desired area of a semiconductor wafer or other targetcan be made very pure since ions of undesirable molecular weight will bedeflected to positions away from the beam and implantation of other thandesired materials can be avoided. The process of selectively separatingions of desired and undesired charge-to-mass ratios is known as massanalysis. Mass analyzers typically employ a mass analysis magnetcreating a dipole magnetic field to deflect various ions in an ion beamvia magnetic deflection in an arcuate passageway which will effectivelyseparate ions of different charge-to-mass ratios.

For shallow depth ion implantation, high current, low energy ion beamsare desirable. In this case, the reduced energies of the ions cause somedifficulties in maintaining convergence of the ion beam due to themutual repulsion of ions bearing a like charge. High current ion beamstypically include a high concentration of similarly charged ions whichtend to diverge due to mutual repulsion. To maintain low energy, highcurrent ion beam integrity at low pressures, a plasma may be created tosurround the ion beam. High energy ion implantation beams typicallypropagate through a weak plasma that is a byproduct of the beaminteractions with the residual or background gas. This plasma tends toneutralize the space charge caused by the ion beam, thereby largelyeliminating transverse electric fields that would otherwise disperse thebeam. However, at low ion beam energies, the probability of ionizingcollisions with the background gas is very low. Moreover, in the dipolemagnetic field of a mass analyzer, plasma diffusion across magneticfield lines is greatly reduced while the diffusion along the directionof the field is unrestricted. Consequently, introduction of additionalplasma to improve low energy beam containment in a mass analyzer islargely futile, since the introduced plasma is quickly diverted alongthe dipole magnetic field lines to the passageway chamber walls.

In ion implantation systems, there remains a need for a beam containmentapparatus and methodologies for use with high current, low energy ionbeams which may be operated at low pressures, and which provides uniformbeam containment along the entire length of a mass analyzer beam guide.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and method forproviding a low energy, high current ion beam for ion implantationapplications. The invention provides ion beam containment without theintroduction of auxiliary plasma and instead enhances beam plasmaassociated with the ion beam by utilizing the background gas in the beamguide to create the additional electrons required for adequate beamcontainment. This is accomplished by providing a multi-cusped magneticfield and RF or microwave energy in a beam guide passageway in order tocreate an ECR condition in a controlled fashion, as illustrated anddescribed in greater detail hereinafter.

Ion beams propagating through a plasma, such as the beam plasma createdby beam interactions with the residual or background gas, reach a steadystate equilibrium wherein charges produced by ionization and chargeexchange are lost to the beam guide. The remaining plasma densityresults from a balance between charge formation due to the probabilityof ionizing collisions, and losses from the beam volume due to repulsionof positive charges by the residual space charge and electron escape asa result of kinetic energy.

Absent plasma enhancement through the introduction of externallygenerated plasma or enhancement of the beam plasma, the probability forionizing collisions with the background gas at very low ion beamenergies is low. Electrons generated in such a manner are trapped in thebeam's large potential well, orbiting around and through the beamcenter, interacting with each other by Coulomb collisions, resulting inthermalization of the electron energy distribution. Those electrons inthe distribution having an energy greater than the ionization potentialof the residual gas molecule have a probability of ionizing such amolecule. The ionizing probability decreases as the electron energydecreases.

In a low energy beam plasma, the majority of the ionization is producedby the trapped electrons. These electrons derive their energy from thecenter-to-edge beam potential difference, which is the same parameterthat causes beam “blow-up”. Thus, transportation of low energy ion beamsis difficult absent externally generated plasma or enhancement of thebeam plasma. Because mass analyzers inherently involve magnetic fields,externally generated plasma fails to diffuse adequately along thearcuate length of a mass analyzer beam guide, instead diffusing quicklyalong the direction of the magnetic field lines. The use of RF ormicrowave energy in a mass analyzer beam guide passageway together witha multi-cusped magnetic field in accordance with the present inventionprovides for enhancement of the beam plasma in a low pressure, lowenergy, high current ion beam system through the controlled creation ofan ECR condition in the passageway. Additionally, the multi-cuspedmagnetic field enhances the plasma density through the magnetic mirroreffect.

Additional plasma may thus be generated within the ion beam space byelectric fields at RF or microwave frequencies. This RF or microwaveenergy is transferred efficiently to plasma electrons, when a propermagnetic field is present, at a magnitude that yields the ECR condition.The RF or microwave energy may be introduced into the passageway at anappropriate port in the beam guide via any number of coupling methods(e.g., windows, antennas, and the like). Although the dipole magneticfield alone might be employed for the creation of an ECR condition, theselection of the dipole magnetic field strength for a mass analysismagnet is dictated by the momentum of the particle selected forimplantation. Consequently, the RF or microwave power source frequencywould need to be tuned to that which provides the ECR conditionaccording to the dipole magnetic field strength.

For example, for very low energy Boron beams, the dipole magnetic fieldis well below the ECR condition at the common 2.45 GHz microwavefrequency. Lower frequency energy sources (or variable frequencysources) are available, but are costly. In addition, there is anadvantage to using the highest available frequency, as the plasmadensity limit is proportional to the square of the frequency employed.Thus, the ability to use a high frequency power source in a low energyion beam application via the selective employment of a controlledmulti-cusped magnetic field allows for higher plasma density as well asreduced cost.

According to one aspect of the invention, the apparatus comprises a massanalysis magnet mounted around a passageway along the path of an ionbeam, an RF power source adapted to provide an electric field in thepassageway, and a magnetic device adapted to provide a multi-cuspedmagnetic field in the passageway. The passageway thus serves as awaveguide as well as a beamguide. According to another aspect of theinvention, the magnetic device comprises a plurality of magnets mountedalong at least a portion of the passageway, whereby the power source andthe magnets cooperatively interact to provide an electron cyclotronresonance (ECR) condition along at least a portion of the passageway.

The multi-cusped magnetic field may be superimposed on the dipole fieldat a specified field strength in a region of the mass analyzerpassageway to interact with an electric field of a known RF or microwavefrequency for a given low energy ion beam. In this manner, the beamplasma within a mass analyzer dipole magnetic field is enhanced for lowenergy ion beams without the introduction of externally generatedplasma. The RF or microwave energy is efficiently transferred to plasmaelectrons in the presence of a magnetic field that yields an ECRcondition. According to one aspect of the present invention, the ECRcondition for a particular ion beam type is dependent upon both theelectric field frequency and the magnetic field strength. However, thedipole magnetic field of the mass analysis magnet is typically fixedaccording to the desired selection of an ion charge-to-mass ratio andthe magnitude of the beam energy to be directed to a target wafer.

The other ECR condition variables being thus fixed, an electric fieldenergy source frequency is thus determined. The creation of amulti-cusped magnetic field in the passageway of a mass analyzeraccording to the present invention advantageously provides localizedcontrol over the magnetic field strength within the passageway, whichallows use of RF or microwave energy sources at common or commerciallyavailable frequencies (e.g., 2.45 GHz). In addition to providing regionsof magnetic field strength which satisfy the ECR condition for anappropriate frequency, the multi-cusped magnetic field also increasesplasma confinement through a magnetic mirror effect, which significantlyenhances the plasma density by reducing losses.

According to another aspect of the invention, the magnetic device maycomprise a plurality of longitudinally spaced laterally extendingmagnets disposed on the top and bottom sides of the mass analyzer beamguide passageway. The magnets may include longitudinally oppositemagnetic poles of opposite magnetic polarity, with poles of likepolarity on adjacent magnets facing one another, whereby the multi-cuspmagnetic field is generated in the passageway. In this manner, an ECRcondition may be established near at least two longitudinally facingmagnetic poles of at least two adjacent magnets and spaced from one ofthe top and bottom sides by a specified distance. The magnets creatingthe multi-cusped field may thus be designed to create an ECR regionspaced from one or more of the passageway walls, providing a controlledconfinement or containment of a passing ion beam.

According to still another aspect of the invention, an ion implantationsystem is provided, which comprises an ion source adapted to produce anion beam along a path and a mass analyzer having an inner passageway.The mass analyzer includes a high frequency power source, a massanalysis magnet mounted in the inner passageway, and a magnetic devicemounted in the inner passageway, wherein the mass analyzer is adapted toreceive the ion beam from the ion source and to direct ions of anappropriate charge-to-mass ratio along the path toward a wafer. The highfrequency power source is adapted to provide an RF or microwave electricfield in the inner passageway, and the magnetic device is adapted toprovide a multi-cusped magnetic field in the inner passageway. Themagnetic device may comprise a plurality of magnets mounted along atleast a portion of the passageway, which generate the multi-cuspedmagnetic field. The magnetic and electric fields may interact to createan ECR condition within the mass analyzer which advantageously enhancesthe beam plasma, thereby neutralizing the space charge of the ion beam.

According to yet another aspect of the invention, there is provided amethod of providing ion beam containment in a low energy ionimplantation system. The method comprises producing an ion beam along alongitudinal path using an ion source, providing a mass analyzer havingan inner passageway and a mass analysis magnet mounted along the innerpassageway, and receiving the ion beam in the mass analyzer from the ionsource. The method further comprises directing ions of appropriatecharge-to-mass ratio and energy from the mass analyzer along the pathtoward a wafer, generating an electric field in the passageway using ahigh frequency power source, and generating a multi-cusped magneticfield in at least a portion of the passageway using a magnetic devicemounted along the passageway. In addition, the method may furthercomprise creating an electron cyclotron resonance condition in at leastone region in the passageway using the electric field and the magneticfield.

The plasma enhancement and the resulting beam containment may be furtheraided by the controlled provision of electric field energy in thepassageway of a mass analyzer. Generating this electric field in thepassageway may be furthered using a separate waveguide to consistentlydistribute the electric field energy within the passageway in acontrolled fashion. In this manner, the energy distribution may be mademore uniform along the longitudinal passageway of the beam guide,allowing creation of electron cyclotron resonance regions throughout theentire length thereof.

According to another aspect of the present invention, there is provideda waveguide for coupling microwave energy from a power source with abeam plasma in a passageway of an ion beam mass analyzer beam guide. Thewaveguide includes a first dielectric layer surrounded by a metalliccoating adapted to propagate microwave energy from the power sourcethroughout the length of the beam guide passageway. The metallic coatingmay thus form a second and third layer on the top and bottom sides ofthe first layer. The first layer extends longitudinally along an arcuatepath in a first plane from an entrance end to an exit end, and laterallybetween an inner radial side and an outer radial side. The waveguidefurther includes laterally extending longitudinally spaced ports orslots through the metallic coating on the side facing the beam guidepassageway. The longitudinally spaced ports or slots may be positionedadvantageously along the waveguide to correspond to the nodes of astanding wave to thereby effectuate an efficient transfer of power tothe beam guide.

In this regard, along the waveguide, a plurality of laterally extendinglongitudinally spaced magnets may be provided which are adapted toprovide a multi-cusped magnetic field in the beam guide passageway. Inthis way, the multi-cusped magnetic field and the microwave energy fromthe power source may cooperatively interact to create an electroncyclotron resonance condition along at least a portion of the passagewayfor beam containment, and the plasma may further be enhanced via themagnetic mirror effect.

According to still another aspect of the invention, a mass analyzer beamguide apparatus is provided for conditioning an ion beam along a path inan ion implantation system. This apparatus comprises a mass analysismagnet mounted in a passageway along the path, a power source adapted toprovide an electric field in the passageway, a waveguide adapted tocouple the electric field with a beam plasma associated with the ionbeam, and a magnetic device adapted to provide a multi-cusped magneticfield in the passageway. Accordingly, the power source, the waveguide,and the magnetic device may be cooperatively adapted to providecontainment of the ion beam in at least a portion of the passageway. Thebeam containment may advantageously be accomplished via an electroncyclotron condition established through the cooperative interaction inthe passageway of an RF or microwave electric field powered by the powersource and the magnetic device, which may create a multi-cusped magneticfield in the interior of the passageway.

According to yet another aspect of the invention, a waveguide isprovided for coupling an electric field with a plasma in an ion beammass analyzer passageway. The waveguide comprises a base layer locatedin a first plane adapted to propagate microwave energy from a powersource, and having a top, bottom, and lateral metallic layers extendinglongitudinally along an arcuate path from an entrance end to an exit endand laterally between an inner radial side and an outer radial side. Thebottom layer may include a plurality of laterally extendinglongitudinally spaced ports or slots therethrough between the interiorof the passageway and the base layer. Microwave energy from the powersource propagating along the base layer is coupled with the plasma inthe interior of the passageway near the laterally extendinglongitudinally spaced ports or slots.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative aspects of theinvention. These aspects are indicative, however, of but a few of thevarious ways in which the principles of the invention may be employed.Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram illustrating a typical low energyion implantation system having a mass analyzer in which the beamcontainment apparatus and methodology of the present invention may beemployed;

FIG. 1B is a schematic view of an ion implanter for ion beam treatmentof a workpiece, including a beam containment apparatus in accordancewith the invention;

FIG. 2 is a top plan view of an exemplary mass analyzer beam guideaccording to an aspect of the invention;

FIG. 3A is an end elevation view of the exemplary mass analyzer of FIG.2 having a plurality of magnets for generating a multi-cusped magneticfield in accordance with another aspect of the invention;

FIG. 3B is a sectional plan view of the exemplary mass analyzer takenalong line 3B—3B of FIG. 3A;

FIG. 4 is a sectional elevation view of the exemplary mass analyzertaken along line 4—4 of FIG. 2;

FIG. 5 is a sectional side elevation view of the exemplary mass analyzertaken along line 5—5 of FIG. 2;

FIG. 6 is a side elevation view illustrating exemplary multi-cuspedmagnetic fields in the exemplary mass analyzer of FIG. 5;

FIG. 7A is a side elevation view in section illustrating anotherexemplary mass analyzer with a waveguide according to another aspect ofthe invention;

FIG. 7B is another side elevation view of the exemplary mass analyzerand waveguide of FIG. 7A;

FIG. 8A is a side elevation view in section illustrating a portion of anexemplary waveguide and magnets in a mass analyzer for generating amulti-cusped magnetic field in accordance with another aspect of theinvention;

FIG. 8B is a sectional top plan view of a portion illustrating theexemplary waveguide and magnets of FIG. 8A;

FIG. 8C is a front elevation view in section taken along line 8C—8C ofFIG. 8B illustrating a portion of the exemplary waveguide of FIGS.8A-8B;

FIG. 8D is another front elevation view in section taken along line8D—8D of FIG. 8B illustrating a portion of the exemplary waveguide ofFIGS. 8A-8C;

FIG. 9 is a sectional top plan view illustrating an exemplary massanalyzer with magnets for generating a multi-cusped magnetic field inaccordance with another aspect of the invention;

FIG. 10 is a top plan view illustrating an exemplary waveguide inaccordance with another aspect of the invention; and

FIG. 11 is a schematic flow diagram illustrating a method of providingion beam containment in an ion implantation system in accordance withanother aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to thedrawings wherein like reference numerals are used to refer to likeelements throughout. The present invention provides for beam containmentin a low energy, high current ion implantation system at low pressureswithout requiring the introduction of externally generated plasma byenhancing the beam plasma using a multi-cusp magnetic field incombination with RF or microwave energy to create an ECR condition in amass analyzer. However, it will be appreciated that the invention may beadvantageously employed in applications other than those illustrated anddescribed herein.

Referring now to the drawings, in FIG. 1A, a low energy ion implanter 10is illustrated, having a terminal 12, a beamline assembly 14, and an endstation 16. The terminal 12 includes an ion source 20 powered by a highvoltage power supply 22. The ion source 20 produces an ion beam 24 whichis provided to the beamline assembly 14. The ion beam 24 is conditionedby a mass analysis magnet 26. The mass analysis magnet 26 passes onlyions of appropriate charge-to-mass ratio to a wafer 30. The conditionedion beam 24 is then directed toward the target wafer 30 in the endstation 16.

Referring also to FIG. 1B, an ion implanter 100 is illustrated ingreater detail in accordance with an exemplary aspect of the presentinvention, and has an ion source 112, a mass analysis magnet 114, abeamline assembly 115, and a target or end station 116. An expansiblestainless steel bellows assembly 118, which permits movement of the endstation 116 with respect to the beamline assembly 115, connects the endstation 116 and the beamline assembly 115. Although FIG. 1B illustratesan ultra low energy (ULE) ion implanter, the present invention hasapplications in other types of implanters as well.

The ion source 112 comprises a plasma chamber 120 and an ion extractorassembly 122. Energy is imparted to an ionizable dopant gas to generateions within the plasma chamber 120. Generally, positive ions aregenerated, although the present invention is applicable to systemswherein negative ions are generated by the source 112. The positive ionsare extracted through a slit in the plasma chamber 120 by the ionextractor assembly 122, which comprises a plurality of electrodes 127.Accordingly, the ion extractor assembly 122 functions to extract a beam128 of positive ions from the plasma chamber 120 and to accelerate theextracted ions into the mass analysis magnet 114.

The mass analysis magnet 114 functions to pass only ions of anappropriate charge-to-mass ratio to the beamline assembly 115, whichcomprises a resolver housing 123 and a beam neutralizer 124. The massanalysis magnet 114 includes a curved beam path 129 within a passageway139 defined by an aluminum beam guide having side walls 130, evacuationof which is provided by a vacuum pump 131. The ion beam 128 thatpropagates along this path 129 is affected by the magnetic fieldgenerated by the mass analysis magnet 114, to reject ions of aninappropriate charge-to-mass ratio. The strength and orientation of thisdipole magnetic field is controlled by control electronics 132 whichadjust the electrical current through the field windings of the magnet114 through a magnet connector 133.

The dipole magnetic field causes the ion beam 128 to move along thecurved beam path 129 from a first or entrance trajectory 134 near theion source 112 to a second or exit trajectory 135 near the resolvinghousing 123. Portions 128′ and 128″ of the beam 128, comprised of ionshaving an inappropriate charge-to-mass ratio, are deflected away fromthe curved trajectory and into the walls of an aluminum beam guide 130.In this manner, the magnet 114 passes to the resolving housing 123 onlythose ions in the beam 128 which have the desired charge-to-mass ratio.

The passageway 139 further comprises a magnetic device including one ormore magnets 170 disposed laterally along the beam path 129. The magnets170 are mounted above and below the beam path 129 to create amulti-cusped magnetic field (not shown in FIG. 1B) in the passageway139. A high frequency electric field (not shown in FIG. 1B) is alsoprovided in the passageway 139 via a microwave injection port 172 whichcouples a power source 174 with the passageway 139. The multi-cuspedmagnetic field and the high frequency electric field in the passageway139 cooperatively interact to create an electron cyclotron resonancecondition in at least one region (not shown in FIG. 1B) of thepassageway in order to provide beam containment of the ion beam 128, asdescribed in greater detail infra.

The resolver housing 123 includes a terminal electrode 137, anelectrostatic lens 138 for focusing the ion beam 128, and a dosimetryindicator such as a Faraday flag 142. The beam neutralizer 124 includesa plasma shower 145 for neutralizing the positive charge that wouldotherwise accumulate on the target wafer as a result of being implantedby the positively charged ion beam 128. The beam neutralizer andresolver housings are evacuated by a vacuum pump 143.

Downstream of the beam neutralizer 124 is the end station 116, whichincludes a disk-shaped wafer support 144 upon which wafers to be treatedare mounted. The wafer support 144 resides in a target plane which isgenerally perpendicularly oriented to the direction of the implant beam.The disc shaped wafer support 144 at the end station 116 is rotated by amotor 146. The ion beam thus strikes wafers mounted to the support asthey move in a circular path. The end station 116 pivots about point162, which is the intersection of the path 164 of the ion beam and thewafer W, so that the target plane is adjustable about this point.

FIG. 2 illustrates an exemplary mass analyzer beam guide 200 for use ina low energy ion implantation system (e.g., low energy ion implanter 10of FIG. 1B), having an arcuate longitudinal passageway 202 defined byinner and outer arcuate side walls 204 and 206, respectively, along anion beam path 208. The beam guide 200 extends longitudinally along thepath 208 from an entrance end 210 to an exit end 212 through an arcangle θ which may be approximately 135 degrees, for example. Beam guide200 further comprises a microwave injection port 214 which providescoupling of RF or microwave energy from a power source 216 with thepassageway 202 via a cable 218.

The beam guide further includes a mass analysis magnet comprising twoarcuate magnet poles (not shown in FIG. 2) to provide a dipole magneticfield in the passageway 202 which allows ions of a selectedcharge-to-mass ratio to reach the exit end 212 along the path 208.

FIGS. 3A and 3B illustrate an end elevation view and a sectional planview, respectively, of the exemplary mass analyzer beam guide 200 ofFIG. 2, having a plurality of magnets 220 associated therewith forgenerating a multi-cusped magnetic field in accordance with an aspect ofthe invention. Magnets 220 extend laterally between an inner radius R1and an outer radius R2 in the passageway 202 in a longitudinally spacedrelationship along the path 208, with an angular spacing θ2, which maybe, for example, 5.326 degrees. In one exemplary implementation of theinvention, the inner radius R1 may be about 300 mm and the outer radiusR2 may be about 500 mm. The passageway 202 is further defined by top andbottom walls 222 and 224, respectively. The dipole field may begenerated externally to the beamguide 200 by an electromagnet (notshown). In another implementation of the invention, the magnets 220 areembedded into one or both of the beamguide walls 222 and 224 in slotsmachined from the outside thereof, such that the magnets 220 remainoutside of the vacuum chamber. In addition, it will be recognized thatmagnets 220 may be provided in one or both of the top and bottom walls222, and 224, respectively, or on one or both of the side walls 204 and206, respectively, or any combination thereof.

FIGS. 4 and 5 respectively illustrate the mass analyzer beam guide 200in longitudinal and lateral section along section lines 4—4 and 5—5 ofFIG. 2. As seen in FIG. 5, magnets 220 are magnetized longitudinallyalong the propagation direction of the ion beam path 208, and arestaggered such that adjacent magnets have like polarity poles facingeach other. For clarity, the magnets 220 having south poles facingtoward the entrance end 210 of the beam guide 200 are indicated as 220Aand magnets 220 having south poles facing toward the exit end 212 of theguide 200 are indicated as 220B. In order to facilitate the massanalysis function, a dipole magnetic field is established in thepassageway 206, for example, via an external electromagnet (not shown)having vertical field lines 230 as illustrated in FIG. 4.

Referring also to FIG. 6, the exemplary bipolar magnets 220A and 220Bcreate individual magnetic fields, illustrated for simplicity withexemplary field lines 232A and 232B which cooperate to form multi-cuspedmagnetic fields near and spaced from the top and bottom walls 222 and224, respectively, in the passageway 206. The exemplary placement ofmagnets 220A and 220B illustrated in the various figures illustratessimilarly oriented magnets 220 vertically aligned (e.g., magnet 220Adirectly above magnet 220A, magnet 220B directly above magnet 220B).However, it will be appreciated that orientations other than thosespecifically illustrated and described herein are possible and arecontemplated as falling within the scope of the present invention.

The orientation of magnets 220A and 220B illustrated in FIGS. 5 and 6,for example, advantageously provides additive magnetic field lines inthe areas between adjacent magnets 220, although this is not requiredfor the invention. Where RF or microwave energy is provided in thepassageway 206 (e.g., via power source 216 and microwave injection port214 of FIG. 2), the cooperative interaction between the magnetic andelectric fields results in the creation of an electron cyclotronresonance (ECR) condition in regions 234 spaced a distance 236A and 236Bfrom the magnets 220.

The ECR condition in regions 234 advantageously provides enhancement ofthe beam plasma associated with an ion beam traveling through thepassageway 206 along the path 208, whereby beam integrity is improvedalong the longitudinal length of the mass analyzer beam guide 200. Thecreation of an ECR condition in one or more regions 234 around an ionbeam prevents beam “blow-up” by facilitating the transfer of energy tothe plasma surrounding the beam, thereby enhancing the plasma. Anelectron cyclotron resonance condition occurs when an alternatingelectric field is applied to a charged particle in a static magneticfield, such that the frequency of the electric field matches the naturalfrequency of rotation of the charged particle around the static magneticfield lines. Where this resonance condition is attained (e.g., inregions 234), a single frequency electromagnetic wave can accelerate acharged particle very efficiently.

It will be appreciated that the sizing, orientation, and spacing of themagnets 220 within the passageway 206 allow the location of the ECRregions 234 to be generated in accordance with desired ion beamcontainment goals. For example, the strength of the magnets 220 may bevaried in order to change the distance 236A and/or 236B between theinner surfaces of the magnets 220 and the ECR regions 234. In thismanner, the distances 236A and 236B may be adjusted according to thepassageway size and/or the desired ion beam size. In addition, thespacing between adjacent magnets 220 may be changed in order to vary thespacing between adjacent ECR regions 234. Furthermore, the relativeorientations of the magnetic pole faces of adjacent magnets may bevaried in order to provide additive magnetic field lines betweenadjacent magnets 220. Many different magnet sizes, orientations, andspacings are possible and contemplated as falling within the scope ofthe present invention.

In accordance with the present invention, the multi-cusped magneticfield employed to obtain the ECR condition may be successfullysuperimposed near the edges of the dipole field. The plasma produced atthe resonance surface where the correct magnetic field strength value isobtained expands toward the center of the ion beam along the dipolefield lines, in a direction opposite to the field gradient. Theintroduction of the electric field into the beam guide passageway 202may further be aided by the use of a waveguide in the passageway asillustrated and described in greater detail infra.

Referring now to FIGS. 7A and 7B, another aspect of the invention isillustrated in reference to mass analyzer beam guide 200, wherein asectional side elevation view is provided. The beam guide 200 comprisestop and bottom walls 222 and 224, respectively, an outer sidewall 206,and an inner side wall (not shown) defining a passageway 202 throughwhich an ion beam (not shown) propagates along a path 208. A pluralityof magnets 220A and 220B (collectively designated as 220) are providedin similar fashion to the magnets 220 of FIGS. 3A-6 which extendlaterally between the inner side wall and the outer side wall 206, in aspaced relationship to each other such that the longitudinally oppositemagnet poles of adjacent magnets 220 face one another. Oriented in thisfashion, the magnets 220 provide a multi-cusped magnetic field in thepassageway 202 near the top and bottom walls 222 and 224, which field isillustrated by exemplary field lines 232A and 232B. A mass analysiselectromagnet (not shown) outside of the beamguide may provide a dipolemagnetic field (not shown) adapted to provide the mass analysisfunctionality discussed supra.

Unlike the mass analyzer implementations in the previous figures, thebeam guide 200 of FIGS. 7A and 7B further comprises one or morewaveguides 250. The waveguide comprises a suitable propagation mediumsuch as quartz, that is metalized on all sides by a thin coating (e.g.,aluminum). Since the skin depth at 2.54 GHz is less than one micrometer,a metalization layer coating thickness of a few microns is adequate.Laterally extending ports or slots 254 are provided in the inwardlyfacing metalization layers of the waveguides 250 between adjacentmagnets 220 for coupling RF or microwave energy from the waveguide 250into the passageway 202 of the beam guide 200 as described in greaterdetail infra. The waveguides 250 may be coupled to an RF or microwavepower source (e.g., source 216 of FIG. 2) through any known method(e.g., windows, antennas, and the like), whereby standing wave resonancemay be established in the waveguides 250 along the longitudinal lengththereof. It will be appreciated that although two waveguides (e.g.,upper and lower) 250 are illustrated in the figures, that otherconfigurations, including a single waveguide 250, may be employedaccording to the invention.

The RF or microwave energy provides electric fields in the passageway202 illustrated by exemplary electric field lines 256A and 256B in FIG.7B which cooperatively interact with the multi-cusped magnetic fieldsgenerated by the magnets 220 to provide ECR regions 234 spaced from thetop and bottom walls 222 and 224. As discussed supra, the ECR conditionpromotes the enhancement of the beam plasma associated with an ion beam(not shown) propagating through the passageway 202 of the beam guide 200along the path 208, whereby the integrity of the beam is maintained bythe reduction or elimination of beam “blow-up”. The ports or slots 254in the waveguide 250 extend laterally between the inner side wall (notshown in FIGS. 7A and 7B) and the outer side wall 206 having a width 260and adjacent ports or slots 254 are longitudinally spaced by an angularpitch distance 262 which is the pitch spacing of the magnets 220.

Referring also to FIGS. 8A and 8B, another exemplary waveguide 250 isillustrated in section, mounted between wall 222 and the multi-cuspedfield magnets 220. According to another aspect of the invention, thewaveguide 250 comprises upper and lower metalized layers 280 and 282,respectively above and below a base layer 284 adapted to propagate RF ormicrowave energy for introduction into the passageway 202 of the beamguide 200. Laterally extending ports or slots 254 are provided in thelower support layer 282 exposing the base layer 284 to the interior ofthe passageway 202. In addition, O-rings 286 may be provided encirclingthe slots 254 in order to seal the magnets from the vacuum region.According to still another exemplary aspect of the invention, the baselayer 284 may be made from quartz, the upper and lower metalized layers280 and 282, respectively, may be made from aluminum, the O-rings 286may be made from a suitable elastomer, and the beam guide cover 288 maybe made from aluminum. Alternatively, however, other materials may beemployed and are contemplated as falling within the scope of the presentinvention.

Referring now to FIGS. 8C and 8D, side section views of the exemplarybeamguide 200 and waveguide 250 are illustrated. In accordance with theinvention, the top wall 222 may include a recess for supporting thewaveguide 250, as well as a seating surface for compressing the o-ring286 around the slot 254. The beamguide 200 may further include a topcover 290 allowing removable mounting of the waveguide 250 in the topwall 222. Referring also to FIG. 8D, the top wall 222 may also include arecess or pocket in which the magnets 220 are seated. The o-rings 286around the slots 254 thus providing for isolation of the magnets fromthe vacuum of the inner passageway 202.

Referring now to FIG. 9, the waveguide 250 is shown installed in a beamguide 200, where the waveguide 250 extends along the path 208 of the ionbeam propagation. The pitch spacing of the magnets 220 is the same asthat of the waveguide ports or slots 254, having an angular value of θ2,for example 5.326 degrees, providing for 25 equally spaced magnets 220along an angular beam guide length of θ1, for example, approximately 135degrees.

In operation, RF or microwave energy (e.g., provided by power source 216via cable 218 and microwave injection port 214) is propagated in thewaveguide 250 located behind the multi-cusped magnetic field generatingmagnets 220. The energy is coupled to the beam plasma (not shown) viathe periodically distributed ports or slots 254 for creation of the ECRcondition (e.g., in regions 234 of FIGS. 7A and 7B) conducive to plasmaenhancement employed for beam containment.

As illustrated further in FIG. 10, the waveguide 250 furthers thegeneration of RF or microwave electric fields of sufficient magnitudeorthogonal to the fixed magnetic fields at many locations (e.g., regions234 of FIGS. 7A and 7B) along the beam propagation path 208. Toward thatend, the length of the waveguide 250 may be set at a multiple of ½wavelengths (e.g., nλ/2, where n is an integer) corresponding to the RFor microwave power source frequency (e.g., 2.45 GHz), with the couplingports or slots 254 located at ½ wavelength locations. The waveguide 250may therefore constitute a resonant structure where standing waves canbe produced therein with the ports or slots 254 located where the Efield is minimum and the H field is maximum (e.g., “H” coupling). Thelength of the ports or slots 254 in the waveguide 250 may be maximized(e.g., slots 254 are nearly as long laterally as the width of thewaveguide 250) and the width may be optimized for nominal impedancematching. For example, in the exemplary waveguide 250, the angular slotspacing (an hence the spacing of the magnets 220) is approximately 5.326degrees, the inner radius R1 is approximately 370 mm, and the outerradius R2 is approximately 430 mm. The length of the ports or slots 254in this example is approximately 50 mm, and the width is approximately 5mm.

In order to obtain consistent electric field patterns in the beam guide200, it is desirable to excite a single dominant propagation mode. Forexample, the TE10 propagation mode for rectangular cross-sectionwaveguides provides an electric field that is normal to the broadwall ofthe guide with a (1) peak in the center of the broadwall. The fieldmagnitude is constant along the direction parallel to the narrow wall(e.g., “0” peaks). This TE10 has the lowest cut-off frequency. Thecut-off frequencies for the TEx0 modes depend only on the broadwalldimension. Higher order modes TEn0 have progressively higher cut-offfrequencies. According to one aspect of the invention, by choosing thesize of the broadwall such that the cut-off frequency for the TE20 modeis slightly larger than the operating frequency (e.g., 2.45 GHZ), thewidest possible waveguide 250 is selected which will only propagate thesingle TE10 mode. Once the waveguide dimensions are so chosen, thepropagation wavelength is determined.

An electric field develops across the ports or slots 254 outside thewaveguide 250 in the interior of the beam guide passageway 202, which isoriented along the ion beam propagation direction (e.g., path 208). Amagnetic field (e.g., multi-cusped field) is generated that isperpendicular to the electric field, with the proper magnitude forcreating the ECR resonance condition in the regions 234 of thepassageway 202. For example, a BF2+ ion beam at an energy of 1.19 keVrequires a magnetic field strength of 873 Gauss to follow the propertrajectory in a mass analyzer of a nominal 400 mm bending radius forcreating the ECR condition. The ECR regions 234 may be locatedadvantageously close enough to the slots 254 in the waveguide 250 tobenefit from the high electric field intensity, yet sufficiently spacedfrom any surface (e.g., magnets 220, waveguide 250, etc.) to minimizeplasma losses. For example, the ECR regions 234 of FIGS. 7A and 7B maybe located a distance 236 away from the magnets 220, which may be in therange of about 4 to 6 mm, with a nominal distance of about 5 mmproviding proper operation.

Referring now to FIG. 11, a method 300 of providing ion beam containmentin a low energy ion implantation system is illustrated. The methodbegins at step 302 wherein an ion beam is produced along a longitudinalpath using an ion source. A mass analyzer is provided at step 304 havingan inner passageway, a high frequency power source, a mass analysismagnet mounted in the inner passageway, and a magnetic device mounted inthe inner passageway. The ion beam is received in the mass analyzer fromthe ion source at step 306, and ions of appropriate charge-to-mass ratioare directed at step 308 from the mass analyzer along the path toward awafer or other target to be implanted with ions. At step 310, anelectric field is generated in the passageway using a high frequencypower source. A multi-cusped magnetic field is generated at step 312using a magnetic device mounted in the passageway, which may createadvantageously an ECR condition therein.

Although the invention has been shown and described with respect to acertain applications and implementations, it will be appreciated thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described components (assemblies, devices,circuits, systems, etc.), the terms (including a reference to a “means”)used to describe such components are intended to correspond, unlessotherwise indicated, to any component which performs the specifiedfunction of the described component (i.e., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure, which performs the function in the herein illustratedexemplary implementations of the invention.

In addition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“includes”, “including”, “has”, “having”, and variants thereof are usedin either the detailed description or the claims, these terms areintended to be inclusive in a manner similar to the term “comprising”.

What is claimed is:
 1. A mass analyzer apparatus for conditioning an ionbeam along a path in an ion implantation system, comprising: a housingdefining a passageway along the path; a mass analysis magnet mountedalong the passageway along the path; a power source adapted to providean electric field in the passageway; and a magnetic device adapted toprovide a multi-cusped magnetic field in the passageway; wherein thepower source and the magnetic device are cooperatively adapted toprovide containment of the ion beam in at least a portion of thepassageway.
 2. The apparatus of claim 1, wherein the magnetic devicecomprises a plurality of magnets mounted along at least the portion ofthe passageway.
 3. The apparatus of claim 1, wherein the power sourceand the magnetic device are cooperatively adapted to provide an electroncyclotron resonance condition along at least the portion of thepassageway.
 4. The apparatus of claim 1, further comprising a top, abottom, and laterally opposite first and second sides defining thepassageway, wherein the top, bottom, first and second sides extendlongitudinally along the path between an entrance end and an exit end,and wherein the magnetic device comprises a plurality of longitudinallyspaced laterally extending magnets disposed in the passageway on one ofthe top and bottom sides between the entrance and exit ends.
 5. Theapparatus of claim 4, further comprising a waveguide extendinglongitudinally along the path between the entrance and exit ends andextending between the plurality of longitudinally spaced magnets and theone of the top and bottom sides of the passageway, and having aplurality of laterally extending slots located between adjacent magnets,wherein the waveguide is adapted to couple energy in the form of anelectric field from the power source to the interior of the passageway,whereby the electric field and the multi-cusped magnetic fieldcooperatively interact to create an electron cyclotron resonancecondition along at least a portion of the passageway.
 6. The apparatusof claim 4, wherein at least two of the magnets include longitudinallyopposite magnetic poles of opposite magnetic polarity and are locatedadjacent one another with poles of like polarity facing one another,whereby the multi-cusp magnetic field is generated thereby in thepassageway.
 7. The apparatus of claim 6, wherein the power source andthe magnetic device are cooperatively adapted to provide an electroncyclotron resonance condition along at least the portion of thepassageway.
 8. The apparatus of claim 1, wherein the magnetic devicecomprises a plurality of longitudinally spaced laterally extendingmagnets disposed in the passageway on both of the top and bottom sidesbetween the entrance and exit ends, wherein the electric field and themagnetic field are cooperatively adapted to create an electron cyclotronresonance condition in at least one region in the passageway, andwherein the at least one region is near at least two longitudinallyfacing magnetic poles of at least two adjacent magnets and spaced fromone of the at least two adjacent magnets by a distance in the range ofabout 4 to 6 mm.
 9. The apparatus of claim 8, wherein the passageway hasa longitudinally arcuate lateral profile.
 10. The apparatus of claim 8,wherein the at least one region is near at least two longitudinallyfacing magnetic poles of at least two adjacent magnets and spaced fromone of the at least two adjacent magnets by a distance of about 5 mm.11. The apparatus of claim 8, wherein the power source provides electricfield energy in the passageway at a fixed frequency of about 2.45 GHZ,and wherein the magnetic field strength in the at least one region inthe passageway is about 873 Gauss, and wherein the ion beam has anenergy of about 1.19 keV.
 12. The apparatus of claim 8, furthercomprising a waveguide extending longitudinally along the path betweenthe entrance and exit ends and extending between the plurality oflongitudinally spaced magnets and one of the top and bottom sides of thepassageway and having a plurality of laterally extending slots locatedbetween adjacent magnets, wherein the waveguide is adapted to coupleenergy in the form of an electric field from the power source to theinterior of the passageway, whereby the electric field and themulti-cusped magnetic field cooperatively interact to create theelectron cyclotron resonance condition along at least a portion of thepassageway.
 13. An ion implantation system, comprising: an ion sourceadapted to produce an ion beam along a path; and a mass analyzer havingan inner passageway, a power source, a mass analysis magnet mounted inthe inner passageway, and a magnetic device mounted in the innerpassageway, wherein the mass analyzer is adapted to receive the ion beamfrom the ion source and to direct ions of appropriate charge-to-massratio along the path toward a wafer, and wherein the power source isadapted to provide an electric field in the inner passageway, and themagnetic device is adapted to provide a multi-cusped magnetic field inthe inner passageway, and further wherein the electric field and themulti-cusped magnetic field cooperatively provide ion beam containmentin at least a portion of the inner passageway.
 14. The system of claim13, wherein the magnetic device comprises a plurality of magnets mountedalong at least a portion of the passageway.
 15. The system of claim 13,wherein the power source provides an electric field in the passageway,wherein the electric field and the multi-cusped magnetic field providean electron cyclotron resonance condition along at least a portion ofthe inner passageway.
 16. The system of claim 13, wherein the massanalyzer further comprises a top, a bottom, and laterally opposite firstand second sides defining the inner passageway, wherein the top, bottom,first and second sides extend longitudinally along the path between anentrance end and an exit end, wherein the magnetic device comprises aplurality of longitudinally spaced laterally extending magnets disposedin the passageway on one of the top and bottom sides between theentrance and exit ends.
 17. The system of claim 16, wherein at least twoof the magnets include longitudinally opposite magnetic poles ofopposite magnetic polarity and are located adjacent one another withpoles of like polarity facing one another, whereby the multi-cuspmagnetic field is generated in the inner passageway.
 18. The system ofclaim 17, wherein the magnetic device comprises a plurality oflongitudinally spaced laterally extending magnets disposed in the innerpassageway on both of the top and bottom sides between the entrance andexit ends, wherein the electric field and the magnetic field create anelectron cyclotron resonance condition in at least one region in theinner passageway, and wherein the at least one region is near at leasttwo longitudinally facing magnetic poles of at least two adjacentmagnets and spaced from one of the top and bottom sides by a distance inthe range of about 4 to 6 mm.
 19. The system of claim 18, furthercomprising a waveguide extending longitudinally along the path betweenthe entrance and exit ends and extending between the plurality oflongitudinally spaced magnets and one of the top and bottom sides of theinner passageway and having a plurality of laterally extending slotslocated between adjacent magnets, wherein the waveguide is adapted tocouple energy in the form of an electric field from the high frequencypower source to the interior of the inner passageway, whereby theelectric field and the multi-cusped magnetic field cooperativelyinteract to create an electron cyclotron resonance condition along atleast a portion of the inner passageway.
 20. The system of claim 18,wherein the at least one region is near at least two longitudinallyfacing magnetic poles of at least two adjacent magnets and spaced fromone of the top and bottom sides by a distance of about 5 mm.
 21. Thesystem of claim 20, wherein the power source provides electric fieldenergy in the inner passageway at a frequency of about 2.45 GHZ, whereinthe magnetic field strength in the at least one region in the innerpassageway is about 873 Gauss, and wherein the ion beam has an energy ofabout 1.19 keV.
 22. A mass analyzer apparatus for conditioning an ionbeam along a path in an ion implantation system, comprising: a massanalysis magnet mounted in a passageway along the path; a fixedfrequency power source adapted to provide an electric field in thepassageway; and a magnetic device adapted to provide a multi-cuspedmagnetic field in the passageway; wherein the fixed frequency powersource and the magnetic device are cooperatively adapted to providecontainment of the ion beam in at least a portion of the passageway. 23.A method of providing ion beam containment in an ion implantationsystem, comprising: producing an ion beam along a longitudinal pathusing an ion source; providing a mass analyzer having an innerpassageway and a mass analysis magnet mounted in the inner passageway;receiving the ion beam in the mass analyzer from the ion source;directing ions of appropriate charge-to-mass ratio from the massanalyzer along the path toward a wafer; and generating an electroncyclotron resonance condition in at least a portion of the innerpassageway, whereby the electron cyclotron resonance condition providesion beam containment thereat.
 24. The method of claim 23, whereingenerating the electron cyclotron resonance condition in at least aportion of the inner passageway comprises: generating an electric fieldin the passageway using a high frequency power source mounted in thepassageway; and generating a multi-cusped magnetic field in at least aportion of the passageway using a magnetic device mounted in thepassageway, wherein the electric field and the multi-cusped magneticfield cooperatively interact to create the electron cyclotron resonancecondition in the at least a portion of the inner passageway.
 25. Themethod of claim 24, wherein the magnetic device comprises a plurality oflongitudinally spaced laterally extending magnets disposed in thepassageway on both of the top and bottom sides between the entrance andexit ends, further comprising creating an electron cyclotron resonancecondition in at least one region in the passageway using the electricfield and the magnetic field, wherein the at least one region is near atleast two longitudinally facing magnetic poles of at least two adjacentmagnets and spaced from one of the top and bottom sides by a distance inthe range of about 4 to 6 mm.